1. Field of the Invention
The present invention relates to a circuit for controlling a latch mode of a pulse width modulation circuit and a method thereof, and particular to a circuit for controlling a latch mode of a pulse width modulation circuit and a method thereof that not only can provide an unlatched voltage which is accurate and is not easily influenced by an external environment of the pulse width modulation circuit, but can also let a user calculate time for the unlatched voltage.
2. Description of the Prior Art
Generally speaking, a pulse width modulation circuit utilizes latch mode protection to prevent an alternating current/direct current converter to which the pulse width modulation circuit is applied from being burned down in an abnormal condition, where the latch mode protection can be over voltage protection, over current protection, over load protection, over temperature protection, and so on. In addition, the prior art utilizes turning-off of an alternating input voltage of the alternating current/direct current converter to let a voltage of a predetermined pin of the pulse width modulation circuit be decreased to a predetermined voltage level, resulting in the latch mode protection of the pulse width modulation circuit being removed.
In the prior art, a stabilizing diode coupled to the predetermined pin of the pulse width modulation circuit is used for setting a voltage level of the predetermined pin of the pulse width modulation circuit after the latch mode protection is removed. However, the prior art has disadvantages as follows: first, the stabilizing diode can increase a chip area of the pulse width modulation circuit; second, the voltage level of the predetermined pin of the pulse width modulation circuit after the latch mode protection is removed is easily influenced by an external environmental temperature of the pulse width modulation circuit; and third, the stabilizing diode usually has a ±5% error.